Electromagnetic device and method of making same



Feb. 15, 1938. R. VERMEULEN ET AL 2,108,275

ELECTROMAGNETIC DEVICE AND METHOD OF MAKING SAME Filed April 17, 1955 2Sheets-Sheet 1 ivwen/fo/Ps HTZ T Y Feb. 15, 1938. R, VERMEULEN ET L2,108,275

ELECTROMAGNETIC DEVICE AND METHOD OF MAKING SAME Filed April :7, 1935 2Sheets-Sheet 2- 10 5 o J 4 3 {a ,o fo 5' o O I By arm/MM Patented Feb.15, 1938 UNITED STATES ELECTROMAGNETIC DEVICE AND METHOD OF MAKING SAMERoelof Vermeulen and Arend Thomas Van Urk, Eindhoven, Netherlands,assignors to N. V. Philips Gloeilampenfabrieken, Eindhoven,

Netherlands Application April 17, 1935, Serial No. 16,872 In Germany May1'7, 1934 6 Claims. (G1. 179100.41)

The present invention relates to electromagnetic devices and to methodsof making same, and pertains more particularly toelectromagnetic-acoustic devices.

The invention will be described in connection with electromagnetic sounddevices for recording, but can be also applied to reproducing devices,etc.

Devices according to the invention are espe- 10 cially well adapted foruse in the method of sound recording described in U. S. Patent No.1,919,116 to J. A. Miller.

In the various electromagnetic devices, for example loudspeakers,pickups and the like in which an armature moves within a magnetic fieldcreated between pole pieces, it is highly important for proper operationthat the armature be accurately spaced from the faces of the polepieces. It is also important that the spaces be easily obtained and onceobtained be maintained irrespective of shocks and vibrations.Furthermore, it is important that the device be easy to assemble anddisassemble even by not highly skilled persons and that the properdistancing of the armature from the pole pieces be efiected withoutrequiring a special device.

In accordance with the invention the pole pieces of the device arerigidly secured to members of nonmagnetic material, which members areprovided with surfaces upon which the armature is suspended; the polefaces and the surfaces of suspension lying in the same plane.

It is necessary that the pole pieces be rigidly secured to the membersof nonmagnetic material so that their relative position thereto will notbe influenced by shock and vibration, and it is preferable that the polefaces and the suspension surfaces be finished in one operation so as tolie in the same plane.

In a particular embodiment of the invention the armature and its meansof suspension form a single piece of magnetic material of uniformthickness. In such a case the armature is mounted on the surface of thenonmagnetic member to which the pole piece is secured, with theinterposition of suitable spacers. In this embodiment of the inventionthe distance between the armature and the pole piece is governed only bythe thickness of the spacer.

Our invention will be more fully described in connection with thespecific example illustrated in the drawings which form part of thespecification, and in which,

Figure 1 is a side elevation of an electromagnetic recorder inaccordance with the invention partly sectionized along line II of Fig.2;

Figure 2 is a side view of Figure 1 partly sectionized along the line11-11 of Fig. 1;

Fig. 3 is a partly sectionized plan view of the 5 recorder shown inFigure l with the upper pole piece assembly removed;

Fig. 4 is a perspective view of one of the pole pieces shown in Figs. 1and. 2, and

Fig. 5 is an exploded perspective view of the 10 recorder of Fig. 1 withthe coils omitted for simplicity.

Referring to Figure 1, the electromagnetic recorder consists of two polepiece assemblies AA, each comprising a U-shaped member E of nonl5magnetic material, for instance copper, and is provided with two planeend-faces 9-9 servin to support an armature l of magnetic material.Rigidly secured to each of the members '|-l for instance by screws,clamping, soldering, or 20 weldingis a pole piece 6 (see Fig. 4) of U-shaped cross section and forming two poles I 8- 18, having pole faces88.

After the pole piece 6 has been secured to the member I, the pole faces8-8 and the faces 9-9 5 are finished so as to lie in the same plane,this being preferably effected in a single operation, for instancebysomilling or grinding the faces 88 and 9-9 that they lie exactly in thesame plane.

The armature I (see Figs. 3 and 5) is formed of 39 a flat piece ofmagnetic material of uniform thickness, for instance of soft iron. Itscentral portion 2 is substantially square and projects on one side in acentrally extension 3, to which a recording cutter or needle I6, isremovably se- 35 cured by means of a screw H. The square 2 of thearmature I extends on each side into narrow neck portions 4-4 to end intwo rectangular suspension portions 5-5 which are provided withclearance holes 2ll2ll. 40

The portions 4-4 serve to provide the torsional forces to the armature;when in operation the armature portion 2 tends to vibrate about thelongitudinal axis of the portions 44.

Arranged one on each side of the portions 4-4 and encircling the portion2 with a clearance sufficient to prevent any contact therewith, are twocoils l2l2. In the case of a recording device as illustrated the coils|2l2 carry the impressed amplified current, whereas for reproducingdevices such coils carry the induced current. In either case the coilsmay be in series or in parallel.

The coils l2--l2 are secured in a fixed position, for example by meansof a wooden wedge I3,

which forces the coils against the inner sides of the poles l8-l8, (seeFig. 2).

The pole piece assemblies AA are arranged with their respective faces 99opposing each other with the interposition of the armature l; the latterbeing spaced from the faces 99 by spacers ID. The whole device issecured together into a rigid unit by four bolts I I, passing throughthe clearance holes 20 of the armature, and through corresponding boresin the members 1---! and in spacers ID.

In the device shown the distance between the surfaces of the armatureportion 2 and the pole faces 88 is determined by the thickness of thespacers I[ll0, and due to this the device may be quickly and accuratelyassembled or taken apart and reassembled Without requiring special toolsor skill.

For mechanical recording the armature I should be comparatively rigidand for this purpose, as has been shown, is made integral with its meansof suspension and has the same thickness. However, in otherelectromagnetic devices, for instance loudspeakers, the armature ispreferably suspended in a less rigid manner. For this purpose, theportions shown as 44 and 5--5 can be made of different material fromthat of the central portions 2, whereby portions 4-4 and 55 are rigidlysecured to the central portion, for instance by soldering or welding.

The magnetic field in which the armature vibrates may be supplied by apermanent magnet l4, secured in good magnetic contact with the polepieces 6-6 by means of screws 15-15. While the magnet I4 is shown ashaving the shape of a bar, magnets of other shapes, for examplehorseshoe magnets, may be also used. Instead of using a permanentmagnet, an electromagnet may also be used, in which case a source ofsupply for energizing the electromagnet is required.

While we have described our invention in regard to specific examples andin specific applications, we do not wish to be limited thereto, butdesire the appended claims to be construed as broadly as permissible inview of the prior art.

What we claim is:

1. An electromagnetic device comprising, a coil, means for producing amagnetic field, a member of non-magnetic material having supportingsurfaces lying in a common plane, a pole piece rigidly secured to saidmember and having pole faces lying in the plane of said supportingsurfaces, an armature adjacently disposed to said pole faces, and meansfor suspending said armature from the supporting surfaces of saidmember.

2. An electromagnetic device comprising, a coil, means for producing amagnetic field, a member of non-magnetic material having supportingsurfaces lying in a common plane, a pole piece rigidly secured to saidmember and having pole faces lying in the plane of said supportingsurfaces, an armature disposed adjacent to said pole faces, and meansincluding spacers for suspending the armature from the supportingsurfaces of said member.

3. An electro-acoustic device for cutting a sound track on a filmcarrier comprising a coil, means for producing a magnetic field, amember of non-magnetic material having supporting surfaces lying in acommon plane, a pole piece rigidly secured to said member and havingpole faces lying in the plane of said supporting surfaces, an armaturedisposed adjacent to said pole faces, a cutting tool connected with saidarmature, and means for suspending said armature from the supportingsurfaces of said member.

4. An electromagnetic device comprising a coil, means for producing amagnetic field, two members of non-magnetic material having supportingsurfaces, the supporting surfaces of each member lying in a commonplane, a pole piece rigidly secured to each of said members and havingpole faces lying in the plane of the supporting surfaces of theirrespective member, an armature disposed adjacent to said pole faces, andmeans for flexibly suspending said armature from the supporting surfacesof said member, said means being clamped between the supporting surfacesof said members.

5. An electromagnetic device, comprising a coil, means for producing amagnetic field, a member of non-magnetic material having supportingsurfaces lying in a common plane, a pole piece rigidly secured to saidmember and having pole faces lying in the plane of said supportingsurfaces, a flat piece of magnetic material of uniform thicknesssuspended from the supporting surfaces of said member with theinterposition of spacers, said fiat piece serving as an armature and asa flexible suspension therefor.

6. An electromagnetic device comprising a coil, means for producing amagnetic field, two U- shaped members of non-magnetic material, eachmember having two supporting surfaces lying in a common plane, a polepiece rigidly secured to each of said members and having two pole faceslying in the plane of the supporting surface of its respectivenon-magnetic member, a fiat piece of magnetic material having a uniformthickness, said piece having an armature portion, suspension portionsand intermediate torsional portions, spacers between said suspensionportions and the supporting surfaces of said non-magnetic members tospace the armature portion from said pole faces, and means for clampingsaid non-magnetic members, spacers and flat piece together.

ROELOF VERMEULEN. AREND THOMAS VAN URK.

